Brown the ground beef in a large pot over medium heat, breaking it up as it cooks. Add the chopped onion and minced garlic, then cook until the onion softens.
Stir in the chili powder and cumin. Cook for one minute until the spices smell fragrant.
Add the drained kidney beans, diced tomatoes, and beef broth. Bring the mixture to a simmer and let it cook uncovered for 10 minutes to thicken slightly.
While the chili simmers, stir together the cornmeal, flour, baking powder, and salt in a bowl. In a separate bowl, whisk the milk, egg, and melted butter. Combine the wet and dry ingredients until just mixed.
Drop spoonfuls of the cornbread batter over the surface of the chili. Cover the pot with a lid and cook on low heat for 15 minutes without lifting the lid. The dumplings are ready when a toothpick inserted in the center comes out clean.